The long-term goal of this project is to understand how solutes and water cross epithelia specialized for fluid transport, such as intestine, stomach, kidney, urinary bladder, and gallbladder. We propose to develop new electrical methods, based on impedance analysis, for simultaneously determining three sets of properties of epithelia: resistances of cell junctions and of apical and basolateral cell membranes; real areas (measured as capacitances) of apical and basolateral membranes; and reflections of ultrastructural geometry, especially membrane folding, in two electrical phenomena termed series resistances and distributed effects. Impedance analysis potentially offers advantages for determining these properties and hence unravelling functional organization in epithelia. Applied noise signals will be used as a rapid technique for studying fast processes and for measuring impedance in small cells. These new techniques will then be applied to studying the functional organization of gastric mucosa, an important and interesting but complicated epithelium whose organization and transport processes have been difficult to study with existing methods.